(1) Field of the Invention
This invention relates to a resolving agent for N-acetylindoline-2-carboxylic acid and a method for preparing an optically active N-acetylindoline-2-carboxylic acid.
(2) Description of the Prior Art
An optically active N-acetylindoline-2-carboxylic acid is used as the intermediate in the preparation of antihypertensive agents, for example, 1-carboxyalkanoyl-L-indoline-2-carboxylic acids. N-Acetylindoline-2-carboxylic acid obtained by chemical synthesis is the racemate and therefore it is necessary to resolve the racemate in order to obtain an optically active N-acetylindoline-2-carboxylic acid.
The prior method for preparing of an optically active N-acetylindoline-2-carboxylic acid includes the use of l-cinchonidine as the resolving agent, as shown in U.S. Pat. No. 4,374,847. The L- optical isomer of N-acetylindoline-2-carboxylic acid is especially important as the optical intermediate of antihypertensive agents, e.g., 1-carboxylalkanoyl-L-indoline-2-carboxylic acids. In the foregoing method, L-optical isomer thereof stays in the mother liquor during the optical resolution, and therefore, in order to obtain L-isomer with high optical purity, the cumbersome operations are inevitable, and it results in undesirably low yield. Additionally, natural l-cinchonidine used as the resolving agent is a relatively expensive and readily not available material on a commercial scale.